The present invention relates to a silver halide photographic lightsensitive material. More particularly, the present invention relates to a silver halide photographic lightsensitive material in which a high-boiling-point organic solvent being excellent in dissolving power, dispersibility, dispersion stability, etc. is used to thereby attain improvement with respect to the deterioration of the color forming properties, and preservability of an emulsion or a latent image with the lapse of time. Hereinafter, a silver halide photographic lightsensitive material is also referred to as a lightsensitive material or sensitive material.
It is common practice to use a photographically useful compound that is sparingly soluble to water by dissolving it in an appropriate oil forming agent, namely a high-boiling-point organic solvent and dispersing the thus obtained solution in a solution of a hydrophilic organic colloid, for example, gelatin in the presence of a surfactant so that the photographically useful compound is contained in a hydrophilic organic colloid layer. Phthalic acid ester compounds and phosphoric acid ester compounds are generally used as the high-boiling-point organic solvent.
The following wide-ranging performances are required of the high-boiling-point organic solvent. For example, the high-boiling-point organic solvent should be excellent in the dissolving power of photographically useful compounds, affinity with gelatin, dispersibility and dispersion stability in gelatin, etc. The high-boiling-point organic solvent should not lower the reactivity of photographically useful compounds, for example, the color forming properties of couplers and the redox reactivity of redox compounds such as color mixing inhibitors. The high-boiling-point organic solvent should enable the optimal regulation of the hue of dyes formed by color forming reactions. The chemical stability of the high-boiling-point organic solvent per se should be excellent. The high-boiling-point organic solvent should not accelerate the decomposition of dispersed photographically useful compounds. The high-boiling-point organic solvent should not accelerate the fading of formed dyes by light, moisture and heat. The high-boiling-point organic solvent should not promote the phenomenon such that photographically useful compounds contained in the lightsensitive material and compounds which are present in processing liquids and, after the processing, remain in the lightsensitive material are decomposed by light, moisture or heat to result in coloring, i.e., staining. The high-boiling-point organic solvent should not shorten the storage life of an emulsion or a latent image. The high-boiling-point organic solvent should be cheap and should be easily procurable.
Phosphoric acid ester high-boiling-point organic solvents can be mentioned as the high-boiling-point organic solvent satisfying the above performance requirements. However, the conventional phosphoric a acid ester high-boiling-point organic solvents are unsatisfactory in various respects. In particular, the deterioration of a color forming properties of a coupler, of an emulsion storage life under humid and hot conditions, and of tone softening which are attributed to the migration of a high-boiling-point organic solvent in lightsensitive material with the laps of time, have been problems of the conventional phosphoric acid ester high-boiling-point organic solvents. Although the migration with the laps of time, can be restrained by the use of a high-boiling-point organic solvent which has a large molecular weight and is highly hydrophobic, the high-boiling-point organic solvent having a large molecular weight has a drawback in that the reactivity of photographically useful compounds such as the color forming properties of coupler is lowered. Thus, it has been difficult to reconcile the anti-diffusing properties and the reactivity for the high-boiling-point organic solvent.
The prior art will now further be described. Although bis type phosphoric acid esters are described in Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 2-125254, JP-A's-2-282250, 5-313327, 61-200538, 62-9348, 63-314543 and U.S. Pat. No. 5,288,715, the structures of these described compounds are different from those of the phosphoric acid esters used in the present invention. In addition, the performances, such as the color forming properties, preservability and dispersibility of a photographic material in which the phosphoric acid esters of the above prior arts are used, were unsatisfactory.
Compounds whose structures are similar to that of the high-boiling-point organic solvent used in the present invention are described in U.S. Pat. Nos. 5,219,510 and 5,104,450. However, these patents only describe supports and mixtures with cellulose esters and are irrelevant to the silver halide photographic lightsensitive material of the present invention.